The purpose of this study is to determine if measuring the amount of CMV in the blood using three new blood tests can predict the development of disease caused by CMV in persons with AIDS. Tests being studied can detect the presence of CMV and also count how much CMV is in the blood. This study will try to determine if people with CMV in their blood are at greater risk for developing CMV disease and to see if a high amount of CMV found means a greater chance of developing CMV disease.